Revise test-device; thresholding and exhaustive checking.

The original version of the test-device could characterise pages
as being grayscale/color purely based on the colorspaces used.

This could easily be upset by grayscale images or shadings that
happened to be specified in non-grayscale colorspaces however.

We now look at the actual shading and image color values, and use
a threshold value to allow for some measure of rounding errors in
color values that are in practice grayscale.

2 files changed, 149 insertions, 21 deletions

diff --git a/source/fitz/test-device.c b/source/fitz/test-device.c
index ffa3917b..d4193c43 100644
--- a/source/fitz/test-device.c
+++ b/source/fitz/test-device.c
@@ -1,21 +1,49 @@
 #include <mupdf/fitz.h>
 
-static void
-fz_test_colorspace(fz_context *ctx, fz_colorspace *colorspace, int *iscolor)
+struct test
+{
+	int *is_color;
+	float threshold;
+};
+
+static int
+is_rgb_color(float threshold, float r, float g, float b)
+{
+	float rg_diff = fz_abs(r - g);
+	float rb_diff = fz_abs(r - b);
+	float gb_diff = fz_abs(g - b);
+	return rg_diff > threshold || rb_diff > threshold || gb_diff > threshold;
+}
+
+static int
+is_rgb_color_u8(int threshold_u8, int r, int g, int b)
 {
-	if (colorspace && colorspace != fz_device_gray(ctx))
-		*iscolor = 1;
+	int rg_diff = fz_absi(r - g);
+	int rb_diff = fz_absi(r - b);
+	int gb_diff = fz_absi(g - b);
+	return rg_diff > threshold_u8 || rb_diff > threshold_u8 || gb_diff > threshold_u8;
 }
 
 static void
-fz_test_color(fz_context *ctx, fz_colorspace *colorspace, float *color, int *iscolor)
+fz_test_color(fz_device *dev, fz_colorspace *colorspace, const float *color)
 {
-	if (!*iscolor && colorspace && colorspace != fz_device_gray(ctx))
+	fz_context *ctx = dev->ctx;
+	struct test *t = dev->user;
+
+	if (!*t->is_color && colorspace && colorspace != fz_device_gray(ctx))
 	{
-		float rgb[3];
-		fz_convert_color(ctx, fz_device_rgb(ctx), rgb, colorspace, color);
-		if (rgb[0] != rgb[1] || rgb[0] != rgb[2])
-			*iscolor = 1;
+		if (colorspace == fz_device_rgb(ctx))
+		{
+			if (is_rgb_color(t->threshold, color[0], color[1], color[2]))
+				*t->is_color = 1;
+		}
+		else
+		{
+			float rgb[3];
+			fz_convert_color(ctx, fz_device_rgb(ctx), rgb, colorspace, color);
+			if (is_rgb_color(t->threshold, rgb[0], rgb[1], rgb[2]))
+				*t->is_color = 1;
+		}
 	}
 }
 
@@ -23,53 +51,153 @@ static void
 fz_test_fill_path(fz_device *dev, fz_path *path, int even_odd, const fz_matrix *ctm,
 	fz_colorspace *colorspace, float *color, float alpha)
 {
-	fz_test_color(dev->ctx, colorspace, color, dev->user);
+	fz_test_color(dev, colorspace, color);
 }
 
 static void
 fz_test_stroke_path(fz_device *dev, fz_path *path, fz_stroke_state *stroke,
 	const fz_matrix *ctm, fz_colorspace *colorspace, float *color, float alpha)
 {
-	fz_test_color(dev->ctx, colorspace, color, dev->user);
+	fz_test_color(dev, colorspace, color);
 }
 
 static void
 fz_test_fill_text(fz_device *dev, fz_text *text, const fz_matrix *ctm,
 	fz_colorspace *colorspace, float *color, float alpha)
 {
-	fz_test_color(dev->ctx, colorspace, color, dev->user);
+	fz_test_color(dev, colorspace, color);
 }
 
 static void
 fz_test_stroke_text(fz_device *dev, fz_text *text, fz_stroke_state *stroke,
 	const fz_matrix *ctm, fz_colorspace *colorspace, float *color, float alpha)
 {
-	fz_test_color(dev->ctx, colorspace, color, dev->user);
+	fz_test_color(dev, colorspace, color);
+}
+
+struct shadearg
+{
+	fz_device *dev;
+	fz_shade *shade;
+};
+
+static void
+prepare_vertex(void *arg0, fz_vertex *v, const float *color)
+{
+	struct shadearg *arg = arg0;
+	fz_device *dev = arg->dev;
+	fz_shade *shade = arg->shade;
+	if (!shade->use_function)
+		fz_test_color(dev, shade->colorspace, color);
 }
 
 static void
 fz_test_fill_shade(fz_device *dev, fz_shade *shade, const fz_matrix *ctm, float alpha)
 {
-	fz_test_colorspace(dev->ctx, shade->colorspace, dev->user);
+	fz_context *ctx = dev->ctx;
+
+	if (shade->use_function)
+	{
+		int i;
+		for (i = 0; i < 256; i++)
+			fz_test_color(dev, shade->colorspace, shade->function[i]);
+	}
+	else
+	{
+		struct shadearg arg;
+		arg.dev = dev;
+		arg.shade = shade;
+		fz_process_mesh(ctx, shade, ctm, prepare_vertex, NULL, &arg);
+	}
 }
 
 static void
 fz_test_fill_image(fz_device *dev, fz_image *image, const fz_matrix *ctm, float alpha)
 {
-	fz_test_colorspace(dev->ctx, image->colorspace, dev->user);
+	fz_context *ctx = dev->ctx;
+	struct test *t = dev->user;
+
+	fz_pixmap *pix;
+	unsigned int count, i, k;
+	unsigned char *s;
+
+	if (*t->is_color || !image->colorspace || image->colorspace == fz_device_gray(ctx))
+		return;
+
+	pix = fz_new_pixmap_from_image(ctx, image, 0, 0);
+	if (pix == NULL) /* Should never happen really, but... */
+		return;
+
+	count = (unsigned int)pix->w * (unsigned int)pix->h;
+	s = pix->samples;
+
+	if (pix->colorspace == fz_device_rgb(ctx))
+	{
+		int threshold_u8 = t->threshold * 255;
+		for (i = 0; i < count; i++)
+		{
+			if (is_rgb_color_u8(threshold_u8, s[0], s[1], s[2]))
+			{
+				*t->is_color = 1;
+				break;
+			}
+			s += 4;
+		}
+	}
+	else
+	{
+		fz_color_converter cc;
+		int n = pix->n-1;
+
+		fz_init_cached_color_converter(ctx, &cc, fz_device_rgb(ctx), pix->colorspace);
+		for (i = 0; i < count; i++)
+		{
+			float cs[FZ_MAX_COLORS];
+			float ds[FZ_MAX_COLORS];
+
+			for (k = 0; k < n; k++)
+				cs[k] = (*s++) / 255.0f;
+			s++;
+
+			cc.convert(&cc, ds, cs);
+
+			if (is_rgb_color(t->threshold, ds[0], ds[1], ds[2]))
+			{
+				*t->is_color = 1;
+				break;
+			}
+		}
+		fz_fin_cached_color_converter(&cc);
+	}
 }
 
 static void
 fz_test_fill_image_mask(fz_device *dev, fz_image *image, const fz_matrix *ctm,
 	fz_colorspace *colorspace, float *color, float alpha)
 {
-	fz_test_color(dev->ctx, colorspace, color, dev->user);
+	/* We assume that at least some of the image pixels are non-zero */
+	fz_test_color(dev, colorspace, color);
 }
 
 fz_device *
-fz_new_test_device(fz_context *ctx, int *iscolor)
+fz_new_test_device(fz_context *ctx, int *is_color, float threshold)
 {
-	fz_device *dev = fz_new_device(ctx, iscolor);
+	struct test *t;
+	fz_device *dev;
+
+	t = fz_malloc_struct(ctx, struct test);
+	t->is_color = is_color;
+	t->threshold = threshold;
+
+	fz_try(ctx)
+	{
+		dev = fz_new_device(ctx, t);
+	}
+	fz_catch(ctx)
+	{
+		fz_free(ctx, t);
+		fz_rethrow(ctx);
+	}
 
 	dev->fill_path = fz_test_fill_path;
 	dev->stroke_path = fz_test_stroke_path;
@@ -79,7 +207,7 @@ fz_new_test_device(fz_context *ctx, int *iscolor)
 	dev->fill_image = fz_test_fill_image;
 	dev->fill_image_mask = fz_test_fill_image_mask;
 
-	*iscolor = 0;
+	*t->is_color = 0;
 
 	return dev;
 }
diff --git a/source/tools/mudraw.c b/source/tools/mudraw.c
index 79092d9c..198e47ce 100644
--- a/source/tools/mudraw.c
+++ b/source/tools/mudraw.c
@@ -316,7 +316,7 @@ static void drawpage(fz_context *ctx, fz_document *doc, int pagenum)
 	if (showfeatures)
 	{
 		int iscolor;
-		dev = fz_new_test_device(ctx, &iscolor);
+		dev = fz_new_test_device(ctx, &iscolor, 0.02f);
 		if (list)
 			fz_run_display_list(list, dev, &fz_identity, &fz_infinite_rect, NULL);
 		else